The present invention is for utilization in connection with oil well drilling apparatus of the conventional type, including a lower well casing, and a blowout preventer stack superimposed on the casing and through which the drill pipe projects for drilling operations. The blowout preventer stack conventionally is surmounted by an upper bell nipple terminating closely beneath the rotary drilling table. The drill pipe string depends from the drilling table downwardly through the bell nipple, the upper annular blowout preventer, one or more ram-type blowout preventers, and into the casing.
The blowout preventers, of course, are intended to seal the annular space between the drill pipe and the string of casing to which the blowout preventer is attached in the event that the pressure within the well bore becomes excessive. Generally, the pressure of the drilling mud introduced into the drill string exceeds the formation pressure in the rocks exposed in the drilled hole. In the event of excess pressure, drilling mud failure, or the like, the blowout preventers are actuated to seal the annular space between the drill pipe and the casing.
It is necessary to test the blowout preventer stack from time to time to ensure proper operation of the preventers. However, repetitive testing by fully actuating the preventers, and particularly in the case of an annular blowout preventer, may well be destructive of the preventers themselves. Further, such testing has not completely tested all of the seals of the blowout preventers, particularly the cap seal of the annular blowout preventer and the top A.P.I. ring groove on the blowout preventer cap. It would be desirable to test each and every connection of the blowout preventer stack without actuating the blowout preventers.
Further, where it is desirable to run wireline tools, as for fishing or snubbing operations, in a complete, conventional drilling rig, it has been necessary either to remove the bell nipple or to close the annular preventer on the wireline lubricator. It would be desirable to adapt the conventional drill string to easy wireline operation without partially dismantling the rig or actuating the preventer.
Also, in temporarily shutting down a well during drilling operations, it has been conventional practice to remove the drill pipe from the casing, to store the drill pipe, and to cap off the casing. This involves considerable expense, the possible theft or damage of the drill pipe during storage at the drilling site, and a delay in restarting drilling operations. It would be desirable to have the capability of storing the drill pipe in the casing itself, where it is safe and quickly available for resumed drilling operations.